Her debut single, Hallelujah, will now be released and is favourite to be the Christmas number one. Bookmakers reported that the show was the biggest reality TV betting event in history. A William Hill spokesman said: "We have never had so many bets on a reality TV programme, with hundreds of first-timers in the shops putting there money on their favourite contestant. The winning song could do the unthinkable and sell a million copies in a week." Alexandra made an unsuccessful contest bid three years ago, but has been widely praised for her performances throughout the live shows.
In the final, she started off singing Christmas carol Silent Night before moving on to the tearjerker Listen with her idol Beyoncé. But it was her version of Leonard Cohen's Hallelujah that settled the contest and won her this year's crown.
It's been an emotional journey for the three finalists. Take a look back at their performances over the past few weeks and relive the final night by clicking through our gallery.